To permit optical interconnections between plural optical components in an optical circuit pack or optical interconnections between plural optical circuit packs or between optical circuit devices on each of which optical circuit packs are mounted, these optical components, optical circuit packs and optical circuit devices are provided at terminals thereof with optical connectors to interconnect them together via optical fibers. As these optical fibers have to be arranged with slacks in this case, it is a current practice that, on an optical circuit pack or inside and/or on a back side of an optical circuit devices, intricately routed lines of the optical fibers extend overlapping one another in the form of a bird's nest and hence occupy a large space. For an optical interconnection process which is complex and requires a large space as descried above, a proposal has been made, as a simple process anywhere routing of optical fibers on a two-dimensional plane as desired. And it has been proposed an optical interconnection apparatus using a sheet or substrate with a pressure-sensitive adhesive coated thereon to hold optical fibers in place by the pressure-sensitive adhesive as disclosed, for example, in JP 2,574,611 B.
Incidentally, the optical interconnection apparatus disclosed in JP 2,574,611 B is obtained in such a way that upon its fabrication, optical fibers are located by a pressure-sensitive adhesive on a substrate (base layer) or on fiber jackets, to form a routing pattern and the routing pattern is then covered with the same material as the material used for the substrate, whereby a protective layer is formed. This process is however accompanied by problems in that as optical fibers so located increase in number and the optical fibers increase more overlapped portions (cross-over routing) in the routing pattern so formed, the resulting routing layer of the optical fibers becomes thicker and, because the tacky surface with which the optical fibers are in contact becomes smaller at the overlapped portions of the optical fibers, the protective layer cannot be arranged evenly. There is a further problem in that at the overlapped portions of the optical fibers in the routing pattern, the fixing force by the pressure-sensitive adhesive becomes weaker and the optical fibers are allowed to move, thereby resulting in displacements in the routing pattern (a loss in the intactness of the routing pattern). The displacements in the routing patterns causes optical loss because of increased possibility of microbending of the optical fibers. Furthermore, when the fixing force by the pressure-sensitive adhesive becomes weak, the optical circuit board becomes extremely weak to breakage which may be caused by deformation such as bending.
In order to solve these problems, it has been attempted to form a protective resin layer on the optical fibers routed on the adhesive layer with a silicone based rubber-like or gel-like material in a fluid state so as to hold the optical fibers intricately routed in place. In such a case, the above-mentioned problems, for example, reduction of fixing force in the overlapped portions of the optical fibers, displacements in the routing pattern, optical loss by microbending of the optical fibers, destruction caused by deformation such as bending can be solved. However, there is another problem that the silicone rubber-like or gel-like material causes attaching, fixing or adhering to the surface of, for example, metal, glass, high polymer (plastic), etc. by its characteristic of tackiness, whereby it becomes impossible to move in the optical interconnection apparatus. Furthermore, there are problems because of its tackiness, that when plural optical interconnection apparatus are piled up upon storage, mounting or transportation, they adhere each other on their surfaces, thereby they being difficult to separate them, and that dust or other substance adheres on the surface of the optical circuit board, when it was installed in a rack or a board. That is, when optical interconnection apparatus is installed in a very narrow space such as in a rack or a board, working efficiency became bad because of its tackiness to result in a problem of being hard to use.
Moreover, since the surface of the formed protective resin layer composed of a silicone based rubber-like or gel-like material is easily broken and damaged, there is a problem of surface scratches when the optical interconnection apparatus is installed in a very narrow space such as in a rack or a board.